Local Number Portability (LNP) allows telephone service subscribers to retain their same directory number, at the same location, when a subscriber changes from one local telephone service provider to another. Telephone number portability was mandated by the Telecommunications Act of 1996.
Telephone calls are routed from a calling subscriber to a called subscriber through the public switched telephone network. A central office switch is used for connecting the subscriber telephone lines. Subscribers connected to a common switch, or End Office (EO) are assigned a unique directory number, commonly referred to as a telephone number. The format of the directory number is NXX-XXXX, where “N” refers to any digit except zero or one and “X” refers to any one of 10 digits. Directory numbers are assigned in blocks of ten thousand to each Local Exchange Carrier (LEC). The first three digits of the directory number are referred to as the exchange code. Each exchange code corresponds to a particular switch or EO. The last four digits of a directory number are referred to as the subscriber's line code. The United States is also divided into “area codes,” more technically referred as Numbering Plan Area (NPA) codes. Thus, each telephone subscriber is associated with a unique 10 digit directory number comprising the three digit NPA code, the three digit exchange code (NXX) plus a four digit line number (XXXX).
The area code and exchange code prefix is used to route the call to the serving End Office. At the End Office, the local switch routes the call to the subscriber's line, which is designated by the last four digits of the directory number. Thus, when a calling party places a telephone call, the first six digits of the dial directory number uniquely identify the terminating switch for the telephone call. The originating switch relies on this relationship to determine the most efficient routing path from the originating switch to the terminating switch at the End Office. Specifically, each switch typically includes a database that cross-references the area code, exchange code prefixes (NPA-NXX) to the various switches. The originating switch then routes the telephone call to the correct terminating switch, which, in turn, further routes the telephone call to the correct subscriber telephone line.
With the passage of the Telecommunications Act of 1996, more than one local telephone service provider in the same geographic area may install and maintain the switching equipment required to provide local telephone service. Indeed, their respective switches can be located in the same building. Local telephone service subscribers can then change their telephone service providers by having the lines servicing their premises disconnected from their previous local telephone service provider and reconnected to their new local telephone service provider. This disconnection and reconnection is referred to as a “cutover,” and may take place at any point in the telephone line circuit to a subscriber's premises. For example, a subscriber line may be cutover at the terminal jack located at the subscriber's premises, at the local telephone service provider's distribution frame, or at any other point in the circuit. Local number portability requires that a subscriber and directory number be re-assigned from the switch associated with the present local telephone service provider to the switch associated with the new local telephone service provider. In a local number portability environment, therefore, the area code-exchange code portion of a directory number will not uniquely identify the switch servicing the line assigned to that directory number. Accordingly, additional telephone call routing procedures are required to allow an originating switch that initially receives a telephone call to determine the correct terminating switch. This is typically accomplished by a LNP database that cross-references individual portable directory numbers to the various switches.
Accordingly, in a LNP environment, originating stations throughout the public switched telephone network refer to their respective LNP databases to determine the terminating stations that service ported subscriber telephone lines. Whenever a subscriber changes local telephone service providers but wishes to maintain the same directory number, all of the LNP databases must be programmed with the porting subscriber directory number and an identification code for the new terminating switch. Until the porting subscriber line is physically cutover from the original terminating switch to the new terminating switch, telephone calls directed to the subscriber directory number must be routed to the prior telephone service provider's terminating switch. After the subscriber line has been cutover, however, telephone calls directed to the subscriber's directory number must be routed to the new telephone service provider's terminating switch. Timing problems, therefore, arise because the physical cutover of the subscriber line occurs at a particular time instant. The various LNP databases, on the other hand, cannot be reprogrammed at the same instant. Thus, subscribers may experience interruptions in phone service until the LNP databases can be updated to reflect the relationship between the subscriber's directory number and the new telephone service provider's terminating switch. In addition, coordinating the physical cutover and database updating imposes scheduling demands upon service provider personnel. Thus, there exists a need for an improved system and method for enabling local number portability.